MB Relationships loses source IDs when processed query arguments are reused

Hi Meta Box team,

I found a reproducible issue in MB Relationships 1.14.0. Reusing a relationship query’s processed arguments in another WP_Query changes the relationship direction and removes its source IDs.

This originally surfaced as missing WP Grid Builder facets on an Etch listing. I subsequently reproduced the underlying failure with Etch, WP Grid Builder, and our compatibility workaround all excluded from the request.

Environment

MB Relationships 1.14.0, bundled with Meta Box AIO 3.13.1
WordPress 7.2-beta1
PHP 8.5.12
WordPress Studio with SQLite

Production MySQL has not been tested. However, you can directly observe the loss of relationship arguments before the resulting SQL runs.

Minimal reproduction

Our fixture has a lfe_clients_projects relationship from Clients to Projects. Client 6679 has four connected projects.

The following is read-only. Substitute a registered relationship, valid source ID, and destination post type from your installation:

$args = [
    'post_type'      => 'lfe_demo_project',
    'post_status'    => 'publish',
    'posts_per_page' => -1,
    'orderby'       => 'title',
    'order'         => 'ASC',
    'relationship'  => [
        'id'   => 'lfe_clients_projects',
        'from' => 6679,
    ],
];

$first = new WP_Query($args);

$normalized_relationship =
    $first->query_vars['relationship'];

// Reuse the processed arguments.
$copied = new WP_Query($first->query_vars);

// Control: reuse the original arguments.
$fresh = new WP_Query($args);

echo wp_json_encode([
    'first_count'             => count($first->posts),
    'normalized_relationship' => $normalized_relationship,
    'copied_count'            => count($copied->posts),
    'copied_relationship'     =>
        $copied->query_vars['relationship'],
    'fresh_count'             => count($fresh->posts),
], JSON_PRETTY_PRINT);

Expected: all three queries return the same four projects.

Actual:

First query: 4 projects
Copied processed args: 0 projects
Original args again: 4 projects

What changes

After the first query, the relationship arguments become:

[
    'id'         => 'lfe_clients_projects',
    'id_field'   => 'ID',
    'direction'  => 'from',
    'items'      => [6679],
    'reciprocal' => false,
    'to'         => null,
]

The original from key has been removed.

After passing those processed arguments to another WP_Query, they become:

[
    'id'         => 'lfe_clients_projects',
    'id_field'   => 'ID',
    'direction'  => 'to',
    'items'      => [],
    'reciprocal' => false,
    'from'       => null,
]

The direction has changed from from to to, and the client ID has disappeared.

The generated join then contains:

INNER JOIN wp_mb_relationships AS mbr ON (
    mbr.from = wp_posts.ID
    AND mbr.type = 'lfe_clients_projects'
    AND mbr.to IN ()
)

Relevant implementation

In inc/query/post.php, MBR_Query_Post::parse_query() normalizes the relationship argument and writes it back into the query variables.

In inc/query/normalizer.php, MBR_Query_Normalizer::normalize_args() determines direction using:

$direction = isset($args['from']) ? 'from' : 'to';

It subsequently removes the selected source key:

unset($args[$direction]);

On a second pass, the original from key no longer exists. The normalizer therefore selects to and overwrites the previously valid direction and items.

Effect on WP Grid Builder

WP Grid Builder calculates facet choices and counts by making additional queries from the listing’s processed query variables.

Its Objects::get_object_ids() passes those variables to Helpers::get_post_ids(), which creates another WP_Query. This exposes the repeated-normalization problem.

In our browser test:

The initial relationship-filtered listing shows the correct projects.

The subsequent facet queries return no IDs.

Facet choices and pagination controls disappear.

Passing the original, unprocessed relationship arguments to the same WP Grid Builder helper returns the correct IDs.

Workaround verification

I tested a separate compatibility plugin that restores the missing source key from the normalized direction and items before Meta Box’s parse_query callback runs.

It leaves fresh arguments unchanged and only repairs recognized, registered relationships in WP Grid Builder-marked post queries.

With that workaround, I verified:

Forward and reverse relationships.

Multiple source IDs and different clients.

Multiple distinct relationships combined with AND or OR.

Empty intersections.

Additional taxonomy and metadata constraints.

Correct browser facet counts, AJAX filtering, and pagination.

The listing still uses live relationships. It does not substitute a stored list of project IDs.

Requested fix

Could the normalizer recognize already-normalized relationship clauses and preserve their source IDs and direction when processing them again?

The same handling should apply to individual clauses in supported AND/OR relationship groups.

Alternatively, preserving the original public relationship arguments in query_vars would prevent subsequent consumers from receiving arguments that cannot safely be reused.

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